1. Field of the Invention
The present invention relates to a magnetron, and more particularly, to a strap in a magnetron.
2. Background of the Related Art
Referring to FIG. 1, a general magnetron is provided with a cylindrical anode. body 11, anode vanes 12 fitted to an inside wall of the anode body 11 in a radial direction, a resonant cavity (not shown) having straps 13 connected to the anode vanes 12 alteratively through two holes 12a and 12b in each of the anode vanes, a cathode 15 on a central portion of the magnetron having a helical filament 14 serving as a cathode 15, an antenna 16 fitted to one of the anode vanes 12, a plurality of cooling fins 17 fitted to an outer circumferential surface of the anode body, a yoke 18a and 18b divided into upper and lower plates for protecting the cooling fins and guiding external air into the cooling fins 17, permanent magnets 19 of N-S poles on top and bottom of the anode body 11 for forming static manetic fields, and a filter box 20 (See FIGS. 2A, 2B.)
The operation of the general magnetron will be explained.
Electrons emitted upon heating the filament 14 receive forces of the static electric field provided between the cathode and the resonant cavity and the static magnetic fields provided in up and down direction of the resonant cavity by the permanent magnets 19, to evolve into a cycloidal movement in an operation space between the cathode and the resonant cavity, when the electrons interact with a high frequency electric field already provided between the anode vanes 12, to move toward the resonant cavity gradually during which most of electron energy is converted into a high frequency energy. The high frequency energy is accumulated in the resonant cavity (not shown) and emitted to outside of the magnetron through an antenna 16. On the other hand, the energies, the electrons are holding, are converted into thermal energies in the resonant cavity. The heat generated at the anode vanes 12 is cooled down by the plurality of cooling fins 17 fitted to the outer circumferential surface of the anode body 11, thereby preventing deterioration of performance of the magnetron caused by the heat.
A first exemplary related art magnetron will be explained based on the foregoing general
Referring to FIGS. 2A and 2B, the first exemplary related art magnetron is provided with two ring form of straps 13 of stainless steel, and a plurality of anode vanes 12 each having two holes 12a and 12b in up and down portions of central portions thereof with the straps 13 passed therethrough. Two pieces of the strap 13 will be called as a first strap and a second strap 13a and 13b, and the two holes 12a and 12b in each of the plurality of anode vanes 12 will be called as a first hole 12a for the smaller one and a second hole 12b for the larger one, which will be explained in more detail. The first strap 13a passes through the first hole 12a in the odd numbered anode vane 12 with contact thereto, and the second hole 12b in the even numbered anode vane without contact thereto according to an order of disposal of the plurality of anode vanes 12, to connect the plurality of the anode vanes 12 at fixed intervals. The second strap 13b passes through the first hole 12a in the even numbered anode vane 12 with contact thereto, and the second hole 12b in the odd numbered anode vane 12 without contact thereto according to an order of disposal of the plurality of anode vanes 12, to connect the plurality of the anode vanes 12 at fixed intervals. The first and second straps 13a and 13b are connected alternatively to odd numbered and even numbered anode vanes respectively, for forming different polarities between adjacent anode vanes 12, to form static electric fields.
However, the related art a magnetron has the following problems.
The straps 13(hereafter called as xe2x80x9ccenter type strapxe2x80x9d) of stainless steel applied to the related art magnetron with a power higher than 1.7KW requires to pass through the anode vanes 12 disposed at fixed intervals one by one, that results in a significant amount of productivity loss. Moreover, the center type strap 13 is required to cut for inserting into the holes 12a and 12b in the anode vanes 13, and to weld the cut ends together once the insertion is completed, when, for good appearance sake, the welding is made at the first hole 12a in the anode vane 12 or the two cut ends are welded the same as an original state, which are inconvenient and complicated in fabrication. Therefore, a simple strapping method is in need, which can solve the foregoing fabrication problem to improve a productivity while characteristics of the strap and the magnetron are equal, or similar to the related art.
Referring to FIGS. 3A and 3B showing a second exemplary related art magnetron for a microwave oven of i KW, the second exemplary related art magnetron is provided with one pair of two ring formed straps 22 with different diameters(the greater diameter strap is called as xe2x80x9couter strap 22bxe2x80x9d, and the smaller diameter strap is called as xe2x80x9cinner strap 22axe2x80x9d) of oxygen free copper(hereafter called as xe2x80x9cside type inner and outer strapsxe2x80x9d), and a plurality of anode vanes 21 each having a notch in top and bottom to form circular grooves in top and bottom of the plurality of anode vanes in overall such that every other anode vane 21 is in contact with the one of the outer strap 22b and the inner strap 22a for inducing a static electric field, which will be explained in detail. The notches in odd numbered anode vanes 21 and even numbered anode vanes 21 are formed to have different shapes(a first notch shape 21a and a second notch shape 21b), such that, with respect to the top side groove, the first notch. shape 21a for the odd numbered anode vane 21 is not come into contact with the inner strap 22a, but with the outer strap 22b, and the second notch shape 21b for the even numbered anode vane 21 is come into contact with the inner strap 22a, but not with the outer strap 22b. The notches in the bottom side have shapes opposite to the top side notches, such that fashion of contact of the inner strap and the outer strap to the odd number and even numbered anode vanes is opposite. Thus, the second exemplary related art strap requires neither the cutting of the strap, nor the insertion of the strap into the holes in the anode vanes, both of which are required in the first exemplary related art magnetron, to permit a high productivity and convenience in fabrication.
However, if a high voltage is applied to the magnetron with the second exemplary related art magnetron for providing a power higher than 1.7KW will cause the following problems. That is, in general, the magnetron has an efficiency of 70% to waste about 30% as heat such that the higher the power of the magnetron, the greater the heat loss wasted at the anode, to cause a problem in securing a thermal stability of the high powered magnetron, particularly, the resonant cavity is subjected to a high thermal stress, of which the most intense part is the very side type inner and outer straps 22, because the inner and outer straps 22 are next to the thermal electrons emitted from the cathode, directly affected by the cycloidal movement of the thermal electrons, and formed of oxygen free copper.
Though the oxygen free copper is used widely owing to its good thermal conductivity, the material is liable to deformation and has a weak strength, such that, if the material is subjected to a relatively high thermal stress, the material is deformed, and the side type strap 22 is broken as fatigue is accumulated from prolonged use. That is, though a stable lifetime of the inner and outer strap 22 of oxygen free copper can be secured within a usual power range of the microwave oven magnetron, it is impossible to apply the inner and outer strap 22 of oxygen free copper to a magnetron having an average high frequency power exceeding 1.7KW.
Accordingly, the present invention is directed to a magnetron that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the magnetron includes a plurality of anode vanes each having notches of shapes different from each other in a top and a bottom, ring formed outer straps of copper each in contact to every other one of the anode vanes in top and bottom notches thereof to connect the anode vanes for forming an electrostatic field to the anode vanes, and ring formed inner straps of a material having a heat resistance higher than the anode vanes of copper and a thermal expansion coefficient similar to the anode vanes each in contact to every other one of the anode vanes in top and bottom notches thereof other than the anode vanes the outer straps are not in contact in concentric with the outer straps on an inner side thereof, thereby preventing deformation and breakage of the straps in advance to allow application to a higher powered magnetron.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.